4^2g GEOLOGY OF CENTRAL WISCONSIN. 



above the adjacent Wisconsin. Tlie eastward slope, on the other 

 hand, is, in Columbia county, very gradual, owing to the general de- 

 scent eastward of the strata. As the watershed turns westward the 

 direction of the dip changes gradually to the south, its amount at the 

 same time becoming lessened. As a result the slopes towards the 

 Catfish valley are again somewhat more abrupt, but never become 

 like those on the Wisconsin side of the divide. 



The western and northern face of this divide, as indicated, forms 

 the eastern and southern side of the Wisconsin valley continuously, 

 from the mouth of the river to the easternmost point of its great 

 bend. Farther north, however, the ridge continues its northeasterly 

 trend, leaving the Wisconsin entirely, and becoming now the eastern 

 boundary of the valley of the upper Fox river as far as Lake Winne- 

 bago. This interesting relation, which is very instructive as to the 

 past conditions of the drainage of these valleys, is finely brought out 

 by the colored Atlas Map of Area E, on which the western edge of 

 the main brown-colored (Lower Magnosian) area, together with the 

 brown lime (Mendota base) just west of it, show the position of the 

 western face of the ridge under consideration. The map will suggest 

 at once, what is in every way the truth, that the valleys of the npper 

 Fox and of the lower Wisconsin are really one. continuous valley, the 

 valley of the upper Wisconsin being an entirely independent one. As 

 already described, the Fox and Wisconsin at Portage traverse a sandy 

 plain within two miles of one another, and without divide of any kind. 

 A glance at the map will show that the Fox makes towards the Wis- 

 consin exactly as do other small tributaries immediately to the 

 south — and from which there is also no divide — then suddenly turn- 

 ing at right angles, passes northward and eastward through a broad 

 valley, out of all proportion to its size. The whole-length of this val- 

 ley bears testimony to the former presence of a great river. The 

 identity of the two valleys is still farther shown by the fact that they 

 constitute one continuous channel of erosion throusrh the same areo- 

 logical formations. The lower Wisconsin is everywhere cut down 

 through the Lower Magnesian limestone, which forms horizontal 

 strata in the upper parts of the high ground on each side. The same 

 formation constitutes the ridge all along the southeast side of the 

 Fox river, and moreover was once spread over the whole country north 

 of that stream, where it is now still found in a few outliers on the 

 very highest ground. The bottoms of both valleys are composed of 

 the Potsdam sandstone. 



The natural inference from these facts is that Lake Winnebago, in- 

 cluding the whole of the great basin of the Wolf, formerly drained 



